Typically a wireless network is configured to transmit on a number of common and dedicated channels. The common channels carry information for a plurality of mobile devices either simultaneously, as through a broadcast, or individually, through independent addressing means. Mobile devices may also be configured to receive a multicast or broadcast signal on a common channel, wherein the multicast or broadcast signal is a message signal generated by a central communication source, such as a computer server, and transmitted simultaneously to a plurality of mobile devices. If a multicast or broadcast service is required to re-transmit the multicast or broadcast information on an individual user basis or to a subset of users, this results in a loss of efficiency for the multicast or broadcast service.
In accordance with third generation partnership project (3GPP) standards, a Universal Mobile Telephoning System (UMTS) network allows operation in four different states in connected mode, CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH. In the CELL_FACH state, the mobile monitors a common physical channel based on some pre-defined selection rules, identified by one or more channelisation codes. The network may map multiple common data channels onto the same common physical channel. The different common channels can be configured differently so as to provide different quality of transmission, typically for different services, over the same common physical channel.
The mobile device typically monitors one of the common channels on an assigned common physical channel. When in the CELL_FACH state, a mobile device is generally available to receive information across a common channel assigned by its network, but must periodically suspend reception of signals on the common physical channel associated with the common channel. These intervals where common physical channel reception is suspended are usually termed measurement occasions. During a measurement occasion, the communications device tunes its receiver to a different frequency for purposes such as measurement of other common physical channel frequencies within the same system or different system. When a measurement occasion occurs, the mobile device typically cannot receive incoming information on the currently allocated common physical channel, due to inherent limitations in receiving two physical channels differentiated in frequency.
Generally, a network seeks to evenly distribute the timing of measurement occasions within a coverage area. This aids in efficient usage of the common physical channels. A typical UTMS network knows the timing of the measurement occasions for the mobiles in a particular cell. Under current UMTS specification 3GPP TS 25.331, the network determines when these measurement occasions are to occur and does not transmit data directed to a particular mobile during the time intervals when that mobile should be in a measurement occasion.
Since different mobile devices will conduct measurement occasions at different times based on their individual identities, the network will not be able to reliably transmit a multicast transmission in an efficient manner that can be completely received by all subscribed mobile devices. Furthermore, if a multicast signal is transmitted on a separate common physical channel, the conventional common data channel may be underutilized and also messages may not be delivered to the mobile device if the mobile device chooses to receive the multicast transmission instead of the transmission destined for it on the conventional common data channels.
Thus, there is a potential conflict between when a mobile device can perform a measurement occasion and the reliable reception of a multicast or broadcast signal. Because each mobile device can perform its measurement occasion at different time intervals, or during different system frames, the multicast or broadcast signal may not be received by mobile devices performing a measurement occasion during a period when the multicast or broadcast is transmitted. Also, if the length of the multicast or broadcast signal is more than one system frame, this increases the number of mobile devices that cannot receive the complete multicast or broadcast signal. Thus, there is a desire to allocate measurement occasions of mobile stations within a coverage area to reduce their impact on multicast or broadcast service reliability and efficiency.